The chemical and physical properties of silicon carbide make it an excellent material for high temperature structural applications. These properties include good oxidation resistance and corrosion behavior, good heat transfer coefficients, low expansion coefficient, high thermal shock resistance and high strength at elevated temperature. It is in particular desirable to produce silicon carbide bodies having high density and suitable for engineering material uses, such as for example high temperature gas turbine applications. Silicon carbide is a preferred material for such use, because it can withstand greater temperature differential than conventional materials, and can therefore lead to greater efficiency in the transformation of energy.
Methods of producing high density silicon carbide bodies have heretofore included reaction bonding (also known as reaction sintering), chemical vapor deposition and hot pressing. Reaction sintering involves the use of silicon impregnants to upgrade the density of the silicon carbide and is useful for many applications, but is undesirable where excess silicon exuding from the silicon carbide body would be detrimental. Silicon carbide deposition is impractical for producing complex shapes, and hot pressing (the production of high density silicon carbide bodies by simultaneous application of heat and pressure) is impractical for some shapes, since the pressure required during the hot pressing operation deforms the silicon carbide body and requires that only relatively simple shapes can be produced by this method.
It is, therefore, an object of this invention to produce a sintered ceramic body having a high proportion of silicon carbide, and a high (greater than 75% theoretical) density. It is a further object of this invention to produce such a body which does not require the use of expensive and hard to obtain finely divided "beta" (cubic) silicon carbide, which has heretofore been regarded as a highly preferred raw material for such ceramic body, due to the previously found difficulties in obtaining sintering of mixtures containing alpha (non-cubic) silicon carbide material.
Subsidiary objects of this invention are the provision of a raw batch and a process for the production of such sintered ceramic body containing high proportion of silicon carbide and high density.